This invention relates to fuel systems for engines and more particularly to a fuel injection system for small internal combustion engines.
Typically, carburetors have been used to supply a fuel and air mixture to both four-stroke and two-stroke small internal combustion engines. For many applications where small two-stroke engines are utilized such as handheld power chain saws, weed trimmers, leaf blowers, garden equipment and the like, carburetors with both a diaphragm fuel delivery pump and a diaphragm fuel metering system have been utilized. In operation, two-stroke engines utilizing these carburetors have a high level of hydrocarbon exhaust emissions which are detrimental to the environment and exceed and cannot meet the exhaust emission requirements imposed by the State of California and the emission requirements proposed by the Environmental Protection Agency of the United States Government and the governments of several other countries.
Due to the relatively low selling price of two-stroke small engines and particularly two-stroke engines for handheld power tools, it is not economically feasible to utilize electronic fuel injection systems such as those typically used for automotive vehicle applications. While various lower cost mechanical fuel injection systems have been proposed for two-stroke small engines, some have either failed to meet the California and proposed emission standards or are economically and/or technically unfeasible for commercial manufacture and sale for two-stroke small engine applications such as handheld power tools.
A fuel injection system for a two-stroke small engine which injects a rich fuel and air mixture directly into the cylinder of the engine. The fuel injection system has a charge forming device which supplies a rich fuel and air mixture to a tuned injector tube connected adjacent one end through a port or valve to the engine cylinder and adjacent the other end to the engine crankcase. The charge forming device has an injector air inlet and fuel mixing passage to which, under engine wide open throttle operating conditions, at least a majority of the fuel is supplied by a high speed fuel circuit and preferably a minor portion of the fuel is also supplied by an idle fuel circuit. Preferably under engine idle conditions the idle circuit also supplies essentially all of the fuel to the engine. Under all engine operating conditions, a separate inlet air flow passage also supplies primary air to the crankcase of the engine from which it is transferred to the cylinder and under engine wide open throttle conditions preferably a very minor quantity of fuel (with a lubricant such as oil therein) is supplied through the engine inlet air flow passage to the crankcase and transferred to the cylinder to provide lubrication of the moving parts in the crankcase and some cooling of the engine. Preferably, fuel is supplied to the high speed, idle and crankcase circuits from a diaphragm type common fuel metering chamber and preferably fuel is supplied to the metering chamber by a diaphragm type fuel pump actuated by pressure pulses in the engine crankcase or the engine inlet air flow passage. Both the fuel injector mixing passage and the engine air flow passage each have throttle valves operably connected together to control in unison and provide proportional air flow through their separate passages. Preferably, both the fuel injector mixing passage and the engine inlet air flow passage also each have choke valves which are operably connected together so that they can be closed and opened in unison and provide proportional air flow through their passages for cold start fuel enrichment of the engine.
Objects, features and advantages of this invention include a fuel injection system for a two-stroke engine providing significantly decreased engine hydrocarbon exhaust emissions, significantly improved fuel economy, increased engine maximum horsepower output, improved engine starting and idle running stability, improved ease, repeatability and stability of calibration and adjustment of the fuel-air ratio and flow rate of the fuel and air mixture, improved combustion stability, synchronized simultaneous throttling of both the engine inlet air flow and the injector inlet air flow, synchronized simultaneous choking for cold starting of both the engine inlet air flow and the injector inlet air flow, improved engine cold starting and warm-up, significantly improved engine performance at elevated ambient temperatures, improved operating stability of the charge forming device over a wide range of orientations and positions of the charge forming device, an extremely compact construction and arrangement, a relatively simple design, extremely low cost when mass produced, and is rugged, durable, reliable, requires little maintenance and adjustment in use, and in service has a long useful life.